Tokkai 6-159157 published by the Japan Patent Office in 1994 discloses a fuel vapor processing device which avoids adverse effects resulting from sloshing on leak diagnosis in a fuel vapor purge vent in a vehicle by suspending leak diagnosis when sloshing occurs.
Sloshing refers to splashing of liquid fuel or inclination of the surface of the liquid fuel in a vehicle fuel tank.
The fuel vapor purge vent comprises a canister absorbing fuel particles from fuel vapor, a passage from the fuel tank to the canister and a passage from the canister to the intake passage for an internal combustion engine. Leaks are diagnosed based on pressure variation after closing the purge vent that was previously regulated to a pressure lower than the atmospheric pressure using the intake negative pressure of the engine intake manifold.
When sloshing occurs during leak diagnosis, the fuel vapor in the fuel tank increases rapidly. As a result, leak diagnosis can not be accurately performed due to the increase in the pressure in the purge vent. Therefore a prior art technique uses pressure variation in the fuel tank to detect onset of sloshing and suspends leak diagnosis while sloshing occurs.